The proposal lists three areas of study concerned with the physiology of synaptic function. 1. Prolonged application of acetylcholine to the frog neuromuscular junction leads to a decrease in the depolarization produced by Ach. One possible mechanism for this desensitization is a block of the channels opened by Ach by an action of Ca ions on the inner surface of the muscle membrane. Attempts will be made to manipulate the intracellular Ca ions level to determine whether the proposed mechanism is valid. Desensitization should be slowed by very low levels of external Ca ions. Muscles buffer internal Ca ions levels quite effectively. However, metabolic poisons and pH changes should increase internal Ca ions, and the affects on Ach sensitivity and the time course of desensitization are to be examined. Other ways to control internal Ca ions, EGTA and Ca injection will also be tried. 2. Preliminary studies of the ion selectivity of the L-glutamate controlled channel of the lobster neuromuscular juncton suggest the possible existence of two types of channels; one is highly selective for Na ions, and the other less so. These findings are to be extended by direct measurement of the reversal potential of the L-glutamate response. The effects of the replacement of Na ion by various cations will be examined to learn more about ion selectivity mechanisms of the channel. The effects of various putative channel blocking agents will also be examined. 3. Release of catecholamine from vesicles within chromaffin cells leads to the appearance of small protrusions, or microspikes, on the cell surface. These may be due to the incorporation of vesicle membrane into the surface membrane during exocytosis. Fluorescent antibodies to two proteins which are in the vesicle membrane, i.e., dopamine beta-hydroxylase and chromomembrin B are to be made. The localization of these antibodies on chromaffin cells induced to release their vesicles should help determine the source of the membrane on the surface of the microspikes.